Perhaps one more opinion won't hurt.
What does it mean, "I trust you, but people with guns make me uncomfortable?"
I would think that this attitude is a reflection of a basic misunderstanding of why people carry. There is a sig floating somewhere on THR that I can't recall to whom it belongs. The gist of that sig is that it's not the odds, it's the stakes, and I believe it sums up nicely why so many choose to carry. It has been my experience however that among those who are uncomfortable around firearms, it is usually because they cannot grasp the motivations of the armed. To these people, an armed LEO is acceptable because the motivation to be armed is clearly understood. A "civilian" (and I do so hate to divide people up with such a vague term) who is armed does not have an easily ascribed motivation. Is a person armed in order to feel empowered to seek out dangerous situations? Or to bolster a flagging self esteem? Will an armed person use their firearm to threaten me or those I care about? Are they armed as an alternative to thoughtful debate?
You'll notice that among the reasons so far listed, self defense is not there. I think that because so few have been in a situation where deadly force would be a reasonable response, they cannot conceive of it as a valid reason. For example, if you use that reason then you must be paranoid, and if paranoid, then you are mentally ill, and if mentally ill, should you be trusted to carry a firearm? If you choose to carry a firearm into my home, where there is absolutely no threat to you, does this not give further proof of your paranoia?
Let's go a little further along this line and assume that your friend does not wish to think you are mentally ill. He sets a boundary that you will not carry into his home; if you agree then maybe you are not crazy and if you do not, then maybe you are.
I like to try to educate people by analogizing to seat belts. I wear a seat belt for several reasons, but never because I am looking to get into an accident. i always hope to never need to be wearing a safety belt, but should the worst happen, I would want to be protected. Unfortunately, the analogy breaks down about that point because safety belts are passive and require no decision making after strapping it on.
And that nicely brings us to the second point of discussion. After understanding motivation, people need to be educated that it is possible for a person other than LEO's or military to be properly trained in the "when" to use firearms as well as the "how" to use firearms. I personally believe that the general population has a very poor understanding of the nature of such training and so ascribe a much higher value to it, even unto bordering on the mystical.
I am a combat vet, and worked in private security for a little while after getting out. As a former armed professional, I have the utmost respect for those currently serving in that capacity. I do not however assume any of them to have god like powers of infallibility or omniscience. We are all human and some of us posses the temperament to pick up arms in the service of others, and some do not. For those that do not, all we can hope to do is to try to educate them that we who do are neither superhuman nor defective.